The primary purpose of OpenMath is to facilitate reliable communication
of mathematical objects between mathematical applications. To
accomplish this the actual meanings of the objects must be available.
To see why consider that in the absence of such definitions we would be
unable to determine if D2y represents two applications of the
differential operator D to the function y, or is simply a monomial
corresponding to the square of the symbol D multiplied by the the
symbol y, where D and y are elements in some algebra chosen by the
author. In this talk we review the current status of the OpenMath
standard, how it is being used, and how this relates to similar
requirements for the communication of mathematical meaning in MathML.